Multiple matrix magnetic separators typically use an annular electromagnetic coil or group of coils to provide a magnetic field volume in the space encompassed by the electromagnetic coils. There is a plurality of magnetic matrices arranged in a stacked array in a container within the space encompassed by the electromagnetic coil. Each magnetic matrix generally includes ferromagnetic material such as steel wool or expanded metal enclosed in the container which may be made of stainless steel or other material of low magnetic permeability. The electromagnetic coil, matrices and container may be enclosed in a ferromagnetic return frame to increase the efficiency of the magnetic circuit. The technique of stacking magnetic matrices adjacent to each other to achieve a predetermined matrix area instead of using a single matrix of the same area is employed to reduce the volume of the ferromagnetic return frame surrounding the coil and thereby reduce the cost of the device, a significant portion of which cost is constituted by the cost of the ferromagnetic return frame. Each additional layer used in the stack to accomplish a particular area requirement reduces the diameter of the top and bottom portions of the return frame, the intermediate cylindrical portion, and the electromagnetic coil and increases the length of the coil and cylindrical portion of the frame in the longitudinal direction of slurry flow through the matrices. The number of matrices used to accomplish a particular process capacity is optimized for maximum efficiency.
Typically the flow in gallons per minute to be processed by a separator is considered in conjunction with the capacity in gallons per minute per unit area of the matrix material. From this the required matrix area is determined and depending on various other considerations that matrix area is accommodated in a stack of two or more matrices. In one approach each matrix in the stack is fed and/or has its separation product removed via inlet and outlet pipes housed in a large circular passage extending through the center of the matrices. This approach is not wholly desirable; it removes from the separation process a substantial area of the matrix used by the passage. In addition as the size of the matrices and the flow rates increase the use of a single large centralized inlet causes problems in wear and abrasion at points where the flow is redirected for submission to the matrix. Further, the use of a single centralized inlet and outlet makes uniform flow distribution a problem. In addition the particular adaptation of each matrix to accommodate the passage and pipes typically requires that each matrix be of a particular configuration dissimilar to the other matrices. Attempts to reduce the size of the central area devoted to the inlet and outlet pipe by using a number of separate smaller pipes entering and leaving radially through the sides of the matrix have met with indifferent success. The electromagnetic coil and magnetic return frame interfere with such side access.